Switch apparatuses are used for transferring data between a plurality of server apparatuses and a plurality of storage apparatuses so that the server apparatuses share the storage apparatuses and data-backup is performed with higher reliability.
Such a switch apparatus includes a plurality of transmission paths for receiving data from any of the server apparatuses and sending the received data to any of the storage apparatuses. The data received by the switch apparatus from the server apparatuses are sent to the transmission paths in the switch apparatus via port modules included in the switch apparatus. The port module is a switch circuit for switching a connection between the transmission path in the switch apparatus and an external apparatus.
The port module sends and receives data. The port module having received data from the external apparatus sends the data to a controller in the switch apparatus. Based on information included in the data received from the port module, the controller sends the data to a port module connected to a destination apparatus. The switch apparatus includes a plurality of controllers. The port module selects one of the controllers, and sends data thereto. Thus, a plurality of transmission paths are present between one port module and another port module.
The port module having data received from the controller sends the data to the storage apparatus connected to the port module.
In the case where a plurality of controllers are present in the switch apparatus, even when one of the controllers fails, the switch apparatus can continue a data sending/receiving process with use of another one of the controllers. However, when the controllers themselves fail during the data sending/receiving, the data being sent/received at the time of failure occurrence are destroyed.
Japanese Laid-open Patent Publication No. 2005-539284 and International Publication Pamphlet No. 91/08632 below each disclose a technology of propagating a signal in a redundant system.